1. Field of the Invention
The present invention relates to a small and thin dynamic pressure bearing, a spindle motor formed by using the dynamic pressure bearing, and a recording disk drive device formed by using the spindle motor.
2. Background Art
Efforts are being made to miniaturize recording disk drive devices, such as hard disk drives, for use in computer equipment, home audiovisual equipment and portable equipment. As such, it has become necessary to reduce the size and thickness of the spindle motor used to rotate the recording disk within the disk drive device.
In the spindle motor for rotating the recording disk, a fluid dynamic pressure bearing is used to meet demands for quietness and long life. In order to support radial loads, substantially V-shaped herringbone grooves are formed in general. By arranging herringbone grooves in two rows in an axial direction, moment stiffness is obtained. However, if the motor is made thin and a radial length of the radial dynamic pressure bearing is reduced, it is difficult to arrange the herringbone grooves in a plurality of rows in the radial direction because of working constraints. However, with a row of grooves, the moment stiffness is insufficient and it is difficult to support the shaft stably.
On the other hand, so-called stepped grooves are employed widely, in which a bearing pitch of the radial bearing is varied in a circumferential direction to thereby support the shaft. With the stepped groove, however, the dynamic pressure is increased in a wide range in an axial direction and therefore sufficient moment stiffness cannot be obtained. For sufficient stiffness, rotational resistance due to generation of dynamic pressure increases and power consumption also increases.
It is an object of the present invention to provide the dynamic pressure bearing with which sufficient radial support of the shaft can be obtained in spite of a short axial length.